Update azure + add GItHub Actions

[rhornung67]

Summary

• This PR affects CI testing on cloud resources only.
• It introduces GitHub Actions testing.
• It adds some issue templates for different types of issues, which may be helpful.
• It updates linux compiler images, moving us off rse-ops images (which are no longer contained) to new radiuss images (which superceded rse-ops).
• It adds several debug builds and several desul atomics builds.
• It attempts to partition testing across both azure and GH Actions platforms for better throughput.

[rhornung67]

Folks, I think this is ready to go. Please review and post on the PR if you have questions, change recommendations, etc.